Thermally stable jet fuel composition

ABSTRACT

Thermally stable turbine or jet fuel composition containing (1) a hydrocarbon polymer of ethylene and a C3 to C4 olefin and optionally a higher olefin and (2) an aldehyde-amine condensation product, and a method for operating a turbine engine.

United States Patent Sweeney et al.

[ Mar. 7, 1972 [54] TIIERMALLY STABLE JET FUEL COMPOSITION [72] Inventors: William M. Sweeney, Wappingers Falls;

Jerzy J. Bialy, Lagrangeville, both of N.Y.

[73] Assignee: Texaco Inc., New York, N.Y.

[22] Filed: May 7, 1969 [2]] Appl. No.: 822,734

[52] US. CL. [51] Int. Cl [58] Field ofSearch ..44/62, 44/73, 44/80 .....C10l 1/16, C101 l/22 ..44/62, 73, 80

[56] References Cited UNITED STATES PATENTS Gee et'al H Churchill et al. A4162 De Vries Primary Examiner-Daniel E. Wyman Assistant Examiner-W. J. Shine Attorney-K. E. Kavanagh and Thomas H. Whaley 9 Claims, No Drawings THERMALLY STABLE JET FUEL COMPOSITION This invention relates to a hydrocarbon fuel composition and, more particularly, to a distillate turbine or jet fuel composition having improved thermal stability.

lt is recognized that petroleum hydrocarbon turbine or jet fuels are susceptible to thermal degradation and oxidation to produce a suspension of finely divided insoluble bodies in the fuel and the formation of deposits on the heat exchanging surfaces. The degree that these undesirable changes take place is dependent on the amount of unstable constituents present in the oil and on the temperature stress and oxidation conditions to which the oil is subjected. The thermal stability rating of the type of fuel compositions in question is determined in a Fuel Coker Test more fully described herein below.

The problem of thermal stability is particularly serious for light hydrocarbon oils which must be maintained at a relatively high temperature for extended periods of time in intimate contact with an oxygen-containing atmosphere. Jet fuels are maintained in such an environment in the wing tanks of aircraft. This problem becomes more acute for jet fuel compositions designed to fuel aircraft having speeds in the Mach 2 and 3 speed ranges or above, such as the forthcoming supersonic transports, because of the substantially higher wing tank temperatures generated.

When a turbine or jet fuel has insufficient thermal stability, degradation takes place one effect being the formation of a suspension of finely divided insoluble bodies. These insoluble bodies are separated from the fuel in the fuel filters of the engine. If there are excessive amounts of insoluble bodies present in the fuel, the fuel line filters become partially or completely blocked resulting in seriously curtailed or lost engine power due to fuel starvation.

The tendency toward deposit formation in a thermally unstable fuel causes a deposits buildup or coking phenomenon commonly referred to as heater tube deposits. This deposits formation seriously interferes with the operation of the fuel-oil heat exchanger in an airplane. It is recognized that the buildup of heater tube deposits cuts down on the heat exchanging efficiency, causes lubricating oil overheat and can lead to engine failure. In supersonic aircraft, the heat exchanger requirements are further increased because of the need to cool the passenger and crew compartments.

A jet fuel composition has now been discovered having substantially improved thermal stability. More particularly, a jet fuel composition has been discovered which exhibits improved thermal stability even after extended high temperature stress while under constant agitation in the presence of air.

ln accordance with this invention, there is provided a fuel composition of enhanced thermal stability containing a minor amount of an additive combination comprising (1) a hydrocarbon polymer i.e., copolymer of ethylene and a C to C olefin or a terpolymer from the foregoing and a higher olefin and (2) a metal deactivator. More particularly, a light hydrocarbon or jet fuel composition is provided containing from about 0.0005 to 0.1 weight percent of a relatively low molecular weight hydrocarbon polymer of ethylene, propylene or butylene and optionally a higher olefin and from about 0.0003 to 0.005 weight percent of an aldehyde-amine condensation product represented by the formula:

OH OH in which R is a divalent hydrocarbyl radical having from two to four carbon atoms.

The hydrocarbon polymer component of the additive combination of this invention is a low molecular weight polymer, such as a copolymer of ethylene and propylene, or ethylene and a butylene, or a terpolymer of ethylene, a C, to C olefin and a C to C; nonconjugated diene. The copolymer and terpolymcrs consist of about to 90 mole percent ethylene and 5 to 70 mole percent propylene or a butylene with the terpolymer also consisting of about 0.1 to 20 mole percent of said diene. The hydrocarbon polymer is an amorphous material and has an Inherent Viscosity in the range from 0.2 to 0.9. A preferred composition of the hydrocarbon polymer is one consisting of from 50 to mole percent ethylene, 5 to 45 mole percent propylene and 1 to 5 mole percent diene and is characterized by an Inherent Viscosity in the range of 0.3 to 0.6. Effective hydrocarbon polymer are disclosed in commonly assigned patent applications wherein they are employed as pour depressants in middle distillates, Ser. No. 513,573 now U.S. Pat. No. 3,524,732 filed 12/13/65, Ser. No.

571,970 now U.S. Pat. No. 3,499,741 filed 8/12/66, Ser. No.

600,013 filed 12/8/66 now U.S. Pat. No. 3,507,636, and Ser. No. 688,672 filed 12/7/67 abandoned in favor of Ser. No. 816,373 filed 4/15/69.

In general, copolymer or terpolymer reactants employed for preparing the additive of the present invention can be produced by a polymerization reaction followed by a cracking reaction. A mixture of ethylene and propylene or ethylene and a butylene and/or a higher olefine or non-conjugated diene in a suitable solvent is polymerized under atmospheric pressure in the presence of a Ziegler-Natta catalyst to produce an amorphous terpolymer product. Suitable butylenes are butene-l, butene-2 and isobutylene. Suitable higher olefins or nonconjugated dienes for the reaction include bicyclo (2,2,1) hepta-2,5-diene, 1,4-cyclohexadiene, 1,5-cyclooctadiene, dicyclopentadiene, diisopropenyl benzene, dipentene, 2,2- dimethyl-l,5-hexadiene, 1,5-heptadiene, 1,5-hexadiene, 2- methyl- 1,4-cyclohexadiene, methylcyclopentadiene dimer, 5- methylene-Z-norborene 3-methyl-l,5-heptadiene, 2-methyl- 1,5-hexadiene, 3-methyl-l,5-hexadiene, 1,7-octadiene, 1,4- pentadiene, 4-vinyl-l-cyclohexene, and 2-methyl-l,4-pentadiene.

The polymerization reaction can be conducted by reacting the olefin mixture under polymerization conditions to produce a polymer having an Inherent Viscosity of at least 1.1. A preferred polymer is one consisting of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 1 to 5 mole percent of a nonconjugated diene having from 6 to 20 carbon atoms and having an Inherent Viscosity in the range of 1.1 to 5. The Inherent Viscosity equals the natural log of the specific viscosity divided by the concentration in grams per ml. The specific viscosity for the equation is the expression of a ration of the viscosity of the solution divided by the viscosity of the solvent (see Appendix D, page 103, Report No. 4 in Polymer Chemistry" by Robert McGovern, Stanford Research Institute, Apr. 1965).

The polymer prepared as above must be cracked to a polymer of reduced lnherent Viscosity. This cracking can be effected by any conventional cracking process, thermal cracking being preferred. Cracking is readily accomplished by heating the terpolymer to a temperature in the range of 250 to 450 C. and holding the terpolymer in this temperature range for a period of time ranging from about 15 seconds to 10 hours. The cracked polymer, which is one component in the present invention, is characterized by having an Inherent Viscosity in the range of 0.2 to 0.9.

Alternatively, a suitable low-inherent Viscosity copolymer or terpolymer can be prepared by polymerizing the olefin components in the presence of hydrogen and a polymerization catalyst to produce a polymer of low-inherent Viscosity in the range disclosed above.

According to other methods for preparing the polymer component for the thermally stable jet fuel, the cracking step can be conducted in the presence of air or oxygen or the cracked product can be treated with air or oxygen at an elevated temperature to modify the properties of the polymer.

The hydrocarbon polymer component is generally employed in the fuel composition in a concentration ranging from about 0.0005 to 0.1 weight percent with the preferred concentration of this component being in the range of 0.001 to 0.005 weight percent, the latter amounts corresponding to about 3 and I5 PTB (pounds per thousand barrels).

The metal deactivator component of this invention is an aldehyde-amine condensation product represented by the formula:

in which R is a divalent hydrocarbyl radical having from two to four carbon atoms. Examples of typical deactivator are N,N-disaIicylidene-l,2-propanediamine and N,N"disalicylidene-l,2-ethane diamine. The metal deactivator is employed in the fuel at a concentration ranging from about 0.0003 to 0.005 weight percent which corresponds to about 0.8 and 14 PTB respectively.

EXAMPLE I A commercial cement consisting of about 3 percent of an ethylene-propylene-dicyclopentadiene terpolymer in hexane, the terpolymer consisting of about 62 mole percent ethylene, 37 mole percent propylene and 1 mole percent dicyclopentadiene and having an Inherent Viscosity of about 2.3 was used. This was washed with 15 percent hydrochloric acid to remove traces of metal remaining from the polymerization catalysts. Then, 30 grams of paraffinic oil having an S.U.S. at I F. of about 100 was added to I liter of the hexane solution. This mixture was stripped of hexane to a pot temperature of 500 F. Air was bubbled in at a rate of 0.2 L/M (liters per minute) and the temperature raised to 667 F. for minutes. The resulting oil mixture contained about 33 percent of the oxidatively cracked terpolymer having an Inherent Viscosity of 0.48.

EXAMPLE II A gas mixture consisting of 25 p.s.i.g. ethylene, 25 p.s.i.g. butylene-l and 5 p.s.i.g. hydrogen was used to saturate 2 liters of heptane at 60 F. 6 ml. of a 20 percent diethylaluminum chloride solution in n-heptane and 2 ml. of a 20 percent solution of tri-n-butyl vanadate in n-heptane were added while polymerization was effected at this temperature over a period of 20 minutes. The reactionproduct was washed with a percent hydrochloric acid solution resulting in the separation of an aqueous layer. 50 grams of cetane and 0.1 gram of 2,6- ditertiarybutyl-4-methylphenol were added and the reaction product then stripped to 500 F. pot temperature. 72 grams of product was recovered consisting of about 30 percent of the copolymer having an Intrinsic Viscosity of about 0.49.

EXAMPLE III A gas mixture consisting of about 33.5 mole percent ethylene, 58.8 mole percent propylene and 7.0 mole percent hydrogen was used to saturate 2 liters of heptane at 74 F. 2 cc. of dicyclopentadiene was added followed by the addition of 8 cc. of a percent solution of diethylaluminum chloride in heptane and 4 cc. of a 20 percent solution of tri-n-butyl vanadate in heptane over a 20 minute period. The reaction product was washed with a 15 percent solution of hydrochloric acid and the aqueous layer separated. 20 grams of mineral oil and 0.1 gram of 2,6-ditertiarybutyl-4-methylphenol were added to the reaction product and the mixture was stripped to 500 F. The reaction product, which had an Inherent Viscosity of 0.33, was recovered as an oil solution containing about 50 percent of the polymer.

The preparation of the turbine or jet fuel composition of the invention simply involves the addition of the two component additive to the fuel in the indicated amounts.

The effectiveness of the fuel compositions of the invention was determined by preparing typical jet fuel compositions and testing for thermal stability in the CFR Fuel Coker Test ASTM-D- 1 660-6 I -T).

The procedure in this coking test requires increasing the severity of the temperature of the preheater tube and fuel filter in 25 F. increments until the fuel fails to pass the test. An important indication of the thermal stability of the fuel composition is the temperature level at which the fuel given performed satisfactorily. The fuel flow was at a rate of 6 lbs. per hour for 5 hours (300 minutes). If the back pressure caused by filter plugging reaches 25.0 inches of mercury before the 300 minutes, the fuel fails this test. For military purposes, a filter pressure of less than 12.0 inches of mercury in 300 minutes is satisfactory (see MIL-.l-5624F). The deposits formed on the tube are rated as from 0 to 4 (where 0 best; 4 worst) depending on the extent of the deposit formation on the tube. A tube rating of 2 or less is satisfactory and a rating greater than 2 fails. v

The base fuel employed in these tests was a typical jet fuel having the following properties:

Gravity, API 43.5 ASTM Distillation, "F

IBP 327 I0 36l 20 374 30 389 40 404 50 419 435 450 467 487 502 EP, 5 l 7 Flash Point F I25 Freezing Point, "F 56 FIA Analysis Aromatics I3.5 Olefins 2.0 saturates 84.5 Net Heat of Combustion BTU/Lb I 8,483 Luminometer Number 5 I .4

The efiectiveness of the additives of the invention in the above jet fuel is shown by the Fuel Coker Test results set forth in the Table below. The concentration of the additive com- TABLE I.ASTM (JOKER THERMAL STABILITY TEST Preheater rated from O-good to 4-bad (a rating of 2 or below passes).

"Filter rating is the pressure in inches of mercury across the filter recorded at the conclusion of the test (300 minutes). If the pressure reaches 25 inches of mercury the test is terminated at that time.

ponents in the fuels is shown in PTB (pounds per thousand barrels of the fuel composition). The concentration of the polymer is shown on the active material basis (minus the diluent oil).

Runs 6, 7 and 8 in the above test are illustrative of the present invention. At the high preheater and filter temperature levels of 450/550 F., the fuel compositions of runs 6, 7 and 8 are the only fuels which qualify as thermally stable by passing both the preheater and filter ratings.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

I. A jet fuel composition comprising a major proportion of a mineral oil distillate, 0.0003 to 0.005 weight percent of I An aldehyde-amine condensation product represented by the formula:

in which R is a divalent hydrocarbyl radical having from two to four carbon atoms, and 0.0005 to 0.1 weight percent of 2. A hydrocarbon polymer selected from the class consisting of A. A copolymer consisting of 50 to 90 mole percent ethylene and the balance propylene or butylene, and

B. A terpolymer consisting of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 0.1 to mole percent of a nonconjugated diene having from five to 30 carbon atoms, said hydrocarbon polymer being amorphous and having an Inherent Viscosity in the range 'of 0.2 to 0.9.

2. A jet fuel composition according to claim 1 in which said condensation product is N,N' -disalicylidene-l,2- propanediamine and said hydrocarbon polymer consists of ethylene and butylene-l 3. A jet fuel composition according to claim 1 in which said condensation product is N,N' -disalicylidene-l,2-

propanediamine and said hydrocarbon polymer consists of ethylene, propylene and dicyclopentadiene.

4. A jet fuel composition according to claim 1 containing from about 0.0003 to 0.005 weight percent of said condensation product and from about 0.0005 to 0.l weight percent of hydrocarbon polymer.

5. A jet fuel composition according to claim 1 in which said hydrocarbon polymer of 50 to mole percent ethylene, S to 45 mole percent propylene and l to 5 mole percent of nonconjugated diene.

6. A jet fuel composition according t claim 1 in which said hydrocarbon polymer consists of about 62 mole percent ethylene, about 37 mole percent propylene and about 1 mole percent dicyclopentadiene.

7. A method for operating a turbine engine which comprises supplying to and burning in said engine a jet fuel composition comprising a major proportion of mineral oil distillate, 0.0003 to 0.005 weight percent of 1. An aldehyde-amine condensation product represented by the formula:

in which R is a divalent hydrocarbyl radical having from two to four carbon atoms, and 0.0005 to 0.1 weight percent of 2. A hydrocarbon polymer selected from the class consistcopolymer consisting of 50 to 90 mole percent ethylene and the balance propylene or butylene, and

B. A terpolymer consisting of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 0.1 to 20 mole percent of a nonconjugated diene having from five to 30 carbon atoms, said hydrocarbon polymer being amorphous and having an lnherent Viscosity in the range of0.2 to 0.9.

8. A method according to claim 7 in which said condensation product is N,N-disalicylidenel ,2-propanediene and said heteropolymer consists of ethylene and butylene-l.

9. A method according to claim 7 in which said condensation product is N,N'-disalicylidene-l,2-propanediamine and said heteropolymer consists of ethylene, propylene and dicyclopentadiene. 

2. A hydrocarbon polymer selected from the class consisting of A. A copolymer consisting of 50 to 90 mole percent ethylene and the balance propylene or butylene, and B. A terpolymer consisting of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 0.1 to 20 mole percent of a nonconjugated diene having from five to 30 carbon atoms, said hydrocarbon polymer being amorphous and having an Inherent Viscosity in the range of 0.2 to 0.9.
 2. A jet fuel composition according to claim 1 in which said condensation product is N,N'' -disalicylidene-1,2-propanediamine and said hydrocarbon polymer consists of ethylene and butylene-1.
 2. A hydrocarbon polymer selected from the class consisting of A. A copolymer consisting of 50 to 90 mole percent ethylene and the balance propylene or butylene, and B. A terpolymer consisting of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 0.1 to 20 mole percent of a nonconjugated diene having from five to 30 carbon atoms, said hydrocarbon polymer being amorphous and having an Inherent Viscosity in the range of 0.2 to 0.9.
 3. A jet fuel composition according to claim 1 in which said condensation product is N,N'' -disalicylidene-1,2-propanediamine and said hydrocarbon polymer consists of ethylene, propylene and dicyclopentadiene.
 4. A jet fuel composition according to claim 1 containing from about 0.0003 to 0.005 weight percent of said condensation product and from about 0.0005 to 0.1 weight percent of hydrocarbon polymer.
 5. A jet fuel composition according to claim 1 in which said hydrocarbon polymer of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 1 to 5 mole percent of nonconjugated diene.
 6. A jet fuel composition according t claim 1 in which said hydrocarbon polymer consists of about 62 mole percent ethylene, about 37 mole percent propylene and about 1 mole percent dicyclopentadiene.
 7. A method for operating a turbine engine which comprises supplying to and burning in said engine a jet fuel composition comprising a major proportion of mineral oil distillate, 0.0003 to 0.005 weight percent of
 8. A method according to claim 7 in which said condensation product is N,N''-disalicylidene-1,2-propanediene and said heteropolymer consists of ethylene and butylene-1.
 9. A method according to claim 7 in which said condensation product is N,N''-disalicylidene-1,2-propanediamine and said heteropolymer consists of ethylene, propylene and dicyclopentadiene. 